When it's one eye it's usually from an injury. I have a couple of my fish get Popeye that way. And they survived it just fine without meds., Out of the three that had Popeye only one required meds.
They do need to be isolated. Then instead of adding Aquarium salt, you need to add Epsom's Salt (it's not really salt it's magnesium) so you don't need to worry about to much salt.
Make sure you do a 50-75% PWC
then add 3-4 Tablespoons of the Epsom's Salt for every 10 gallons of water. Then do 50% PWC
every day for 3 days replacing the Epsom's Salt each time.
The ES will reduce the swelling of the eye there by preventing further damage from the pressure. When the Popeye is from an injury, reducing the swelling will allow the eye to heal on it own.
If there is no improvement after the three days, then continue the ES and PWC
but add an antibiotic specifically for Popeye.
Once again Maracyn makes a great paper weight. Seachem makes a great med for Popeye called Kanaplex. It's easy to use and won't affect any of your good bacteria, nor will it change colors. it's great stuff.
I have African cichlids and they do fight on occasion. I won't use anything but Seachem meds. their great.
Good luck, and whether it's from an injury or from a bacterial infection, in order for it to heal and prevent further damage you must reduce the swelling of the eye/eyes!